A Massachusetts federal judge made an “erroneous decision” when he struck down the federal definition of marriage as between one man and one woman, said a conservative, pro-family group.

Judge Joseph Tauro ruled Thursday that the federal ban on gay marriage is unconstitutional because it interferes with a state’s right to define marriage.

But Liberty Counsel founder Mathew Staver, who is also dean of Liberty University School of Law, argues that the federal Defense of Marriage Act (DOMA) does not prohibit states from defining marriage. DOMA states that for federal purposes, marriage is between one man and one woman. Therefore, federal benefits for spouses apply only to heterosexual marriages.

“Every court until now that has considered the federal Defense of Marriage Act has found it to be constitutional,” said Staver in a statement. “This activist decision must be appealed, and when appealed, I am confident it will be reversed.”

Liberty Counsel has defended the definition of marriage in more than 45 cases and has never lost a challenge involving the federal DOMA.

Tauro’s ruling allows for gay marriage partners in Massachusetts to receive the same federal benefits as heterosexual married couples.

The Boston-based judge ruled that “as irrational prejudice plainly never constitutes a legitimate government interest,” DOMA violates the Equal Protection Clause under the Fifth Amendment. He simultaneously ruled in a separate lawsuit that the DOMA definition of marriage violates the Tenth Amendment rights of states to be sovereign, and the U.S. Constitution’s Spending Clause. The cases were filed by Gay & Lesbian Advocates & Defenders and Massachusetts Attorney General Martha Coakley, respectively.

“While the American people have made it unmistakably clear that they want to preserve marriage as the legal union of one man and one woman, liberals and activist judges are not content to let the people decide,” commented Tom McClusky, senior vice president of Family Research Council. “We look forward to higher court review and reversal of this erroneous decision.”

The Defense of Marriage Act was enacted in 1996 with the support of an overwhelming majority in the House, 342 to 67, and in the Senate, 85 to 14. It was then signed by President Bill Clinton. The Obama administration, however, has called for the repeal of DOMA.

McClusky noted that Judge Tauro’s decision is partly a result of the “deliberately weak legal defense of DOMA” by the government under the Obama administration.

The Justice Department said it is reviewing Judge Tuaro’s decision and has not stated if it plans to appeal or not.

The DOMA ruling in Massachusetts could trigger similar cases in the other five states and the District of Columbia that also legally recognize gay marriage.

Same-sex marriage has been legal in Massachusetts for more than six years. Massachusetts was the first state in the nation to legally recognize such unions.